Multifunctional information terminal devices (simply called “information terminal devices” below) such as smartphone can operate lots of applications and thus are convenient. However, abuse of personal information when such an information terminal device is taken by a stranger and privacy issues are becoming serious problems.
From this point of view, typical information terminal devices in recent years have, for example, a function of automatically changing to a state (called “locked state” below), in which all applications are inactive, when no input operation has been detected for a specific period of time. In order to return from such a locked state to a state in which the applications can be used normally, some information terminal devices are designed to request an operation of inputting unlocking information for user authentication (i.e., an unlocking operation).
For the unlocking operation, the user is often requested to display an unlocking screen, which is utilized for unlocking, on a display unit and then input the unlocking information (which requires secrecy) onto the unlocking screen. However, an authentication process requiring such multiple inputting steps is complicated and increases the risk of the unlocking information viewed by a stranger (i.e., information leakage).
As a technique related to the locking function, an information terminal device has been proposed in which in the authentication process for the unlocking, a preregistered specific piece of music is reproduced, and authentication is performed by inputting a predetermined operation in accordance with a rhythm pattern of the reproduced music (Patent Document 1).
Accordingly, the user can input password information in a simpler manner while ensuring confidentiality. In addition, Patent Document 1 proposes a function of making only a specific function among the functions of the information terminal device be limitedly available based on the authentication process according to the rhythm pattern.